The present invention relates to an electronic apparatus which copes with an EMC which is becoming more and more important in increasing speed and packaging density of IC and LSI devices, and to a device, a circuit board and an electronic apparatus which require suppression means for spurious radiation noise and a method of making the same.
An EMC intends to the compatibility of an electromagnetic environment of an EMI (noise source) and an immunity (noise receiver). Recently, the rise of an operating frequency due to high performance of a product raises a radiation intensity of spurious radiation, which leads the EMI to a severe situation. Further, with the population of the electronic products, the countermeasure for the EMI of the electronic products is becoming severer.
It is reported that the increase of the anticipated spurious radiation amounts to 4 dB/year. If the spurious radiation increases in this manner, the electromagnetic environment becomes more and more worse and it is no doubt that a television video screen is disturbed or a manipulation system of an aircraft becomes uncontrollable and social problems are raised.
For this reason, a noise regulation in terms of a radiation intensity and a scope of applicable products is more and more enhanced and manufacturers are endeavoring to enhance the EMC performance of the products by design and simulation prediction technique to clear the regulation.
As a technical reference relating thereto, JP-A-3-14284 is cited. The JP-A-3-14284 discloses a built-in structure to a printed circuit board in place of discrete parts of a ferrite core and a ferrite beads which are existing countermeasure parts.
In order to enhance the EMC performance of the product, various countermeasure parts such as a common mode choke, a filter and a bypass capacitor for an I/O unit and a power supply have been used from the past but these parts present demerits of {circle around (1)} increase of a cost, {circle around (2)} problem to so-called high packaging density such as minituarization, thinning and weight reduction of a product due to the increase of volume, {circle around (3)} complexity of the countermeasure part, and {circle around (4)} restriction to external view design.
Further, in such a prior art product, the conformity to the future increase of the spurious radiation due to the rise of the operation frequency of the product is restricted.
The restriction to the suppression of the spurious radiation from the electronic apparatus by using the countermeasure parts is explained for a case of a bypass capacitor.
As examples of means for suppressing the spurious radiation form the electronic apparatus, the suppression of a potential fluctuation of a ground system which serves as a drive source for an antenna and the insertion of a common mode core to a cable are cited. Of those, the means for suppressing the potential fluctuation includes a method for using a bypass capacitor.
FIG. 13 shows a sectional structure model of a four-layer circuit board using a bypass capacitor. The four-layer circuit board comprises a signal layer (S1), a power layer (V), a ground layer (G) and a signal layer (S2). In FIG. 13, a dielectric material layer is omitted. As externally connected circuit components, a device equivalent circuit comprising a series connection of an inductance Ld, a load resistor Rd and a switch SW and a power equivalent circuit comprising a series connection of a bypass capacitor having a capacitance of C0, a DC power supply E0 and an inductance Lg are included. In the circuit board, a stray capacity C1 by the power layer (V) and the ground layer (G) and inductances L0 and L1 by a wiring pattern and through-holes are formed.
The bypass capacitor is provided in order to absorb the potential fluctuation as described before.
FIG. 14 shows an equivalent circuit of the sectional structure model shown in FIG. 13.
Since the potential fluctuation V0 occurs in a power lead of an IC device at the switching of the IC device (modeled by ON/OFF of SW in FIG. 14), the bypass capacitor is provided to absorb the potential fluctuation V0.
However, since the inductances L0 and L1 due to the wiring pattern and the through-holes for connecting the bypass capacitor C0 are included by the nature of the circuit board structure, a resonance loop is created with the stray capacity C1 and the effective suppression of the potential fluctuation may be difficult.
Namely, as the operation frequency rises and harmonics frequencies rise, the bypass capacitor does not exhibit the inherent capacitance characteristic because of its inductive component and it cannot absorb the potential fluctuation of the ground system.
Namely, as the operating frequency of the electronic product rises, the prior art technique cannot cope with the future increase of the spurious radiation.
As other countermeasure means, plating may be applied to a plastic housing to form a shield structure to suppress the spurious radiation as seen in a modern notebook type personal computer, but the shield structure has demerits of {circle around (1)} increase of cost and {circle around (2)} the reduction of added value of the product by a problem to recycling the plastic housing.
Thus, new countermeasure means for suppressing the spurious radiation without lowering the added value of the electronic apparatus has been demanded, and on the other hand, a mechanism of the spurious radiation has not been fully investigated. As described in the Technical Journal of the Association of Electronics and Electronic Communications of Japan, EMCJ 94-88 (1995-3), the investigation of a radiation source model for a common mode radiation is behind and it is a future problem to be solved.
It is an object of the present invention to provide an electronic apparatus which suppresses spurious radiation at a level of a circuit board mounted on the apparatus.
It is a second object of the present invention to provide a structure of a circuit board to be applied to an electronic apparatus.
It is a third object of the present invention to provides a circuit board and a method of manufacturing the same when the structure of the present invention is applied to various manufacturing methods.
In order to achieve the first object of the present invention, an electronic apparatus is provided with a circuit board suppressing spurious radiation is formed by providing first and second ground layers having at least one thereof electrically connected to electrical parts, a power layer provided between said first ground layer and said second ground layer and electrically connected to said electronic parts, a dielectric material layer for joining said second ground layer and said power layer and a resistor layer having said first ground layer and said second ground layer electrically connected, and said circuit board is housed in a housing.
Alternatively, an electronic apparatus is provided with a circuit board suppressing spurious radiation is formed by providing a ground layer and a power layer electrically connected to electronic parts, a dielectric material layer for connecting said second ground layer and said power layer, and a first dielectric material layer and a second dielectric material layer sandwiching said ground layer and said power layer therebetween, and said circuit board is housed in a housing.
In order to achieve the second object of the present invention, a structure is characterized by the provision of a first conductor layer and a second conductor layer; a third conductor layer provided between said first conductor layer and said second conductor layer; a first dielectric material layer for joining said first conductor layer and said third conductor layer; a second dielectric material layer for joining said second conductor layer and said third conductor layer; and a resistor for joining said first conductor layer and said second conductor layer.
Alternatively, a structure is provided with a first conductor layer, a second conductor layer, a dielectric material layer provided between said first conductor layer and said second conductor layer, and a resistor layer
Specifically, the structure is provided with a first conductor layer, a second conductor layer, a third conductor layer, a first dielectric material layer, a second dielectric material layer and a resistor layer, and characterized in that said second conductor layer sandwiched by said first dielectric material layer and said second dielectric material layer and said resistor layer are arranged between said first conductor layer and said third conductor layer; and a capacitor C formed by a series connection, through said second conductor layer, of a capacitor C1 formed by arranging said first dielectric material layer between said first conductor layer and said second conductor layer and a capacitor C2 formed by arranging said second dielectric material layer between said second conductor layer and said third conductor layer, and a resistor R formed by arranging said resistor layer around said second conductor layer sandwiched by said first dielectric material layer and said second dielectric material layer form a parallel circuit.
Alternatively, the structure is provided with a first conductor layer, a second conductor layer, a first dielectric material layer, a second dielectric material layer and a resistor layer, and characterized in that said first dielectric material layer and said second dielectric material layer are arranged between said first conductor layer and said second conductor layer; and said resistor layer is sandwiched by said first dielectric material layer and said second dielectric material layer.
When the former structure is specifically viewed in terms of function, the structure is characterized by the provision of a first conductor layer and a second conductor layer; a third conductor layer provided between said first conductor layer and said second conductor layer; a first dielectric material layer for joining said first conductor layer and said third conductor layer; a second dielectric material layer for joining said second conductor layer and said third conductor layer; and a resistor for joining said first conductor layer and said second conductor layer, and the resistor is arranged such that the Q value of the structure is within a predetermined value.
Alternatively, the structure is characterized by the provision of a first conductor layer and a second conductor layer; a third conductor layer provided between said first conductor layer and said second conductor layer; a first dielectric material layer for joining said first conductor layer and said third conductor layer; a second dielectric material layer for joining said second conductor layer and said third conductor layer; and a resistor for joining said first conductor layer and said second conductor layer, and the resistor is arranged to matching terminate the parallel plate line formed by said first conductor layer and said second conductor layer.
In order to achieve the third object of the present invention, a method of manufacturing a circuit board is characterized by steps of forming a multi-layer circuit board having a circuit board comprising at least a ground layer and power layer or a multi-layer structure of said circuit board; and forming a resistor layer on a side of said circuit board or said multilayer circuit board, or at least a portion of an outer periphery of a wiring area in said ground layer and said power layer.
Alternatively, a circuit board is provided with a first conductor layer, a second conductor layer, a third conductor layer, a first dielectric material layer, a second dielectric material layer and a resistor layer, and characterized in that said second conductor layer and said resistor layer are sandwiched between said first dielectric material layer and said second dielectric material layer and arranged between said first conductor layer and said third conductor layer; a metallic layer is used as said conductor layer, an inorganic or organic material is used as said dielectric material layer and an inorganic material layer is used as said resistor layer in forming a low EMI circuit comprising a capacitor component and a resistor component on the circuit board between said first conductor layer and said third conductor layer and said layers are stacked on the circuit board to form a multilayer wiring structure; a wall shape structure made of conductors is formed in a self-closed line shape in an outer periphery of the dielectric material layer on the circuit board on in the dielectric material layer; and a plurality of conductor layers of different structures are electrically connected through the resistor layer.
Alternatively, in a low EMI circuit having a structure in which a power conductor layer and a resistor layer are held between two ground conductor layers, said power conductor layer is arranged to the two ground conductor layers through a dielectric material layer, said resistor layer is arranged in a periphery of said dielectric material layer and connected to the two ground conductor layers, a method of manufacturing a circuit board comprising the steps of forming the conductor layer by a thick film printing method of conductor paste which is a mixture of a metal comprising silver (Ag), palladium (pd), copper (Cu), gold (Ag) or an alloy thereof or a mixture thereof and organic polymer resin solved in organic solvent; forming the resistor layer by the thick film printing method of resistor paste which is a mixture of ruthenium oxide (RuO2) or a compound including ruthenium oxide and organic polymer resin solved in organic solvent; glass ceramic is used as the low dielectric constant dielectric material layer and perovskite type ferro-dielctric material is used as the high specific dielectric constant dielectric material layer.
First, a principle of the present invention for suppressing the spurious radiation from the electronic radiation is explained.
The spurious radiation from the electronic apparatus generally includes two radiation modes, differential mode radiation and common mode radiation.
For example, for the circuit board which is a center of noise sources, the differential mode radiation is created by a current flowing in a loop formed by the conductor pattern and the loop serves as a miniature antenna for generating a magnetic field. On the other hand, the common mode radiation is created by the potential fluctuation of the ground system, and when an external cable in connected, it serves as an antenna for generating an electrical field.
The differential mode radiation may cope with by the design or the layout but the common mode radiation is caused by the potential fluctuation of the ground system and it is difficult to suppers it because it is not intended by the design. In addition, the common mode radiation is a big factor in determining the radiation performance of the circuit board and the product using the same.
In the electronic apparatus of the present invention, the common mode radiation is suppressed at the level of the circuit board to suppress the spurious radiation from the electronic apparatus. Namely, the circuit board which suppresses the spurious radiation is constructed by xe2x80x9cproviding first and second ground layers having at least one thereof electrically connected to electrical parts, a power layer provided between said first ground layer and said second ground layer and electrically connected to said electronic parts, a dielectric material layer for joining said second ground layer and said power layer and a resistor layer having said first ground layer and said second ground layer electrically connectedxe2x80x9d or xe2x80x9ca ground layer and a power layer electrically connected to electronic parts, a dielectric material layer for connecting said second ground layer and said power layer, and a first dielectric material layer and a second dielectric material layer sandwiching said ground layer and said power layer therebetweenxe2x80x9d, and said circuit board is housed in a housing to suppress the common mode radiation at the level of the circuit board to suppress the spurious radiation emitted from the electronic apparatus.
The present invention aims to suppress the spurious radiation at the level of the circuit board, and it eliminates various countermeasure parts such as a common mode choke, a filter and a bypass capacitor for an I/O unit and a power code which have been required in the prior art, and solves the problems of {circle around (1)} the increase of cost of the electronic apparatus, {circle around (2)} problems to so-called high packaging density such as minituarization, thinning and weight reduction of the product due to the increase of volume, {circle around (3)} the complexity of the countermeasure parts, and {circle around (4)} the restriction to the external design.
Further, since a design without the shield structure having plating applied to the plastic housing as seen in the modern notebook type personal computer is allowed, the shield structure is eliminated and {circle around (1)} the reduction of cost and {circle around (2)} the recycling of the plastic housing may be attained.
By providing the prior art countermeasure parts in the electronic apparatus of the present invention, it is natural to cope with the future increase of the spurious radiation and provide a highly reliable electronic apparatus against the spurious radiation.
A structure or a circuit board of the present invention for suppressing the spurious radiation at the level of the circuit board is now explained.
While the mechanism of the radiation source model for the common mode radiation is not fully investigated, the inventors of the present invention assumed that it is the potential fluctuation caused between the power layer and the ground layer and attempted to absorb the potential fluctuation by providing a resistor (resistive layer). The potential fluctuation depends on a drive frequency of the electronic parts mounted on the circuit board and the structure or the circuit board of the present invention is handled for two major modes, {circle around (1)} a lumped constant circuit and {circle around (2)} a distributed constant circuit although the basic constructions are substantially identical for both circuits.
The operation of the structure or the circuit board of the present invention as the lumped constant circuit is first explained.
In the structure or the circuit board of the present invention, in FIG. 14, in order to absorb the potential fluctuation V1 generated between the power layer (V (and the ground layer (G), a resistor Rc formed in the circuit board is connected to the capacitor C1 to form a parallel circuit (see FIG. 2) or a series circuit (see FIG. 12) of the capacitor C1 and the resistor Rc to reduce a Q value (attain Q value of not larger than 10).
For the parallel circuit, since it is difficult to directly connect the resistor Rc between the power layer (V) and the ground layer (G), another ground layer and a capacitor C2 are formed and the resistor Rc and the capacitor C2 are serially connected to block a DC component. By making an impedance of the capacitor C2 sufficiently small for frequencies in a radiation suppression area, a parallel circuit of the capacitor C1 and the resistor Rc is effectively formed (C2 in FIG. 4 may be neglected and a circuit of FIG. 5 is formed).
Namely, when the structure or the circuit board of the present invention functions as the lamp constant circuit, the low Q-value is attained by providing the resistor to absorb the potential fluctuation.
The function of the structure or the circuit board of the present invention as the distributed constant circuit is now explained.
In FIG. 13, in order to absorb a standing wave generated between the power layer (V) and the ground layers (G, G1), a further ground layer (G2) and the resistor (resistor layer) are used and a parallel plate line is formed by the two ground layers (G1, G2) arranged to sandwich the power layer (V), and a matching termination resistance RO is given by the resistor (resistor layer) arranged at the line end.
In this case, since the two parallel plate lines formed by the power layer (V) and the ground layer (G1) and other ground layer (G2) have the line ends thereof opened, a large potential fluctuation occurs at the end in a particular frequency region. However, since it is arranged in the parallel plate line formed by the two ground layers (G1, G2), the standing wave due to the potential fluctuation is absorbed by the matching termination resistor R0.
Namely, when the structure or the circuit board of the present invention functions as the distributed constant circuit, the matching termination is made by the resistor to absorb the potential fluctuation due to the resonance of the standing wave.
As a condition for the matching termination, a resistance r of the resistor should be set to meet the following relation:
R=(h/a)xc2x7{square root over ((xcexc0xc2x7xcexcr1)/(xcex50xc2x7xcex5r1))}
where
h: gap length between G1-V
a: length of one side of rectangle
xcex50: dielectric constant in vacuum (air)
xcex5r1: specific dielectric constant of dielectric material filled between G1-V
xcexc0: permeability in vacuum (air)
xcexcr1: specific permeability of dielectric material
A further effect may be attained by adding the following condition in the above structure.
In the structure of matching termination, the capacitance c2 of the second dielectric material layer is set such that the second conductive layer and the third conductive layer are at the same potential so that the fluctuation of the third conductive layer (power layer) may be absorbed by the resistor.
In the above structure, when the resistance R of the resistor and the capacitance C2 of the second dielectric material layer meet the following relation, the Q-value of the structure may be lowered:
R greater than 1/xcfx89C2
where
C2=xcex50*xcex5r2*S/d
w: angular frequency (area) required for low EMI
xcex50: dielectric constant in vacuum (air)
xcex5r2: specific dielectric constant of dielectric material filled between G2-V
S: area of dielectric material
d: gap length between G2-V
Similarly, when the resistance R of the above resistor and the capacitance C1 of the first dielectric material layer meet the following relation, the Q-value of the structure may be set to a desired value:
Q≈xcfx89*C1*R 
where
xcfx89: angular frequency area required for low EMI
Further, in the above structure, when the first dielectric material layer and the second dielectric material layer are formed by the same dielectric material, the warp of the circuit board may be reduced.
Further, in the above structure, when high speed signal layer (fifth conductor layer) is provided between the ground layer (first conductor layer) and the power layer (third conductor layer), it is necessary that the second dielectric material layer is formed by a dielectric material of a low dielectric constant.
In the above structures, when the power layer is surrounded by the two ground layers and the resistor (resistor layer), the potential fluctuation and the standing wave generated between the solid layers of the power layer and the ground layer may also be absorbed and shielded.
When only the low Q is to be attained, the resistor may be approached to the conductor from the formula defining the Q-value.